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    <script>
        // let arr = [1,[4,5,6],2,[7,8,9],3];

        // let arr2 = arr.flat();

        // console.log(arr); 
        // console.log(arr2); 

        // let arr = [1,[4,['a','b','c'],5,6],2,[7,8,9],3];

        // console.log(arr.flat(3));

        let arr = [1,[2,[3,[4,[5,[6,[7]]]]]]];

        console.log(arr.flat(Infinity));

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